1. Field of the Invention
This invention relates to a data reproducing apparatus and more particularly to an apparatus of the kind reproducing main information data from a tape-shaped record bearing medium on which many recording tracks are formed with additional information data also recorded along with the main information data in a given position in the recording tracks.
2. Description of the Related Art
A typical example of apparatus of the above-stated kind, as disclosed in this specification, is an audio tape recorder which is arranged to record, using digital modification and time compression techniques, by means of a rotary head, an audio signal as a main information signal.
FIG. 1 of the accompanying drawings shows by way of example the tape transport system of the conventional audio tape recorder of the above-stated kind. The illustration includes a magnetic tape 1; and a rotary cylinder 2 which carries rotary heads 3 and 4. The heads 3 and 4 are thus arranged to obliquely trace the tape 1 to record an audio signal on the tape. Six recording areas are arranged to extend in the longitudinal direction of the tape 1. Every time the heads 3 and 4 revolve 36 degrees, the audio signal is recorded in each of the six areas with time base compression. The tape recorder is thus arranged to be capable of recording audio signals in a total of six channels.
A brief description of this tape recorder is as follows: While the tape transport system is as shown in FIG. 1, FIG. 2 shows the recording loci of the tape recorder on the tape 1. Referring to FIG. 2, while the head 3 or 4 is tracing parts between points A and B, points B and C, points C and D, points D and E, points E and F and points F and G as shown in FIG. 1, the audio signal is recorded in the areas CH1 to CH6. It is possible to record the audio signal in each of these areas separately from another area. In each of these areas, recording is carried out in a manner called azimuth overlapped writing. The recording tracks within each of the areas CH1 to CH6 do not have to be perfectly aligned. Further, in each area, pilot signals are recorded for the purpose of tracking control. These pilot signals respectively have one of different frequencies f1 to f4. These different pilot signals are recorded in rotation in the following sequence of frequencies: f1.fwdarw.f2.fwdarw.f3.fwdarw.f4.fwdarw.within, each of these areas. However, the pilot signals in these areas have no correlation with each other.
A recording or reproducing operation is arranged to be performed in the areas CH1, CH2 and CH3 while the tape 1 is allowed to travel at a given speed in the direction of arrow 7 and to be performed in other areas CH4, CH5 and CH6 while the tape is allowed to travel in the direction of arrow 9 as shown in FIG. 1. As a result of this difference in the traveling direction of the tape, the inclination of recording tracks formed in the areas CH1 to CH3 somewhat differs from that of recording tracks formed in other areas CH4 to CH6 as shown in FIG. 2. However, a difference arising between these two groups of areas in the relative speed of the tape and the head due to the travelling speed of the tape 1 is very small and ignorable as compared with a difference due to the revolution of the heads 3 and 4.
FIG. 3 is a time chart showing the recording and reproducing operations of the conventional tape recorder which is arranged as described above. In FIG. 3, signal (a) represents a phase detection pulse signal generated in synchronism with the rotation of the cylinder (hereinafter referred to as PG signal (a)). The PG signal (a) is in a rectangular wave form which repeats a high level (hereinafter referred to as H level) and a low level (hereinafter referred to as L level) in a cycle of 1/60 sec. A signal (b) represents another PG signal which is of an opposite polarity to the PG signal (a). The PG signal (a) is at an H level during the revolution of the head 3 from the point B to the point G of FIG. 1. The PG signal (b) is also at an H level while the other head 4 is revolving between the points B and G.
A signal (c) of FIG. 3 represents a pulse signal obtained from the PG signal (a). Said pulse signal indicates a timing of sampling the audio signal of a period corresponding to one field portion (1/60 sec.) of a video signal for every other field. A signal (d) represents a pulse signal indicative of a timing for addition of a redundant code for correcting an error of the one-field portion of the audio data (or signal) sampled by using a RAM or the like for that purpose. The signal (d) is at an H level during this signal processing period. A signal (e) represents pulses the H level of which indicates a period of time for recording the above-stated signal processed data on the tape 1. The temporal flow of signals shown in FIG. 3 is as described below:
The data sampled during a period between points of time t1 and t3 (during the movement of the head 3 from the point B to the point G of FIG. 1) is subjected to a signal processing operation during a period between points of time t3 and t5 (while the head 3 is moving from the point G to the point A) and is recorded during a period between points of time t5 and t6 (while the head 3 is moving from the point A to the point B). In other words, the data is recorded in the area CH1 of FIG. 2 by the head 3. Meanwhile, the data sampled while the PG signal (b) is at an H level is subjected to a signal processing operation at a timing similar to the timing mentioned above and is then recorded in the area CH1 of the tape by the head 4.
A signal (f) of FIG. 3 represents another PG signal which is obtained by shifting the phase of the PG signal (a) to a given extent (to an extent of 36.degree. which corresponds to one recording area in this instance). In recording an audio signal according to this PG signal (f) and a further PG signal which is of an opposite polarity to the PG signal (f), the conventional tape recorder operates as follows: Audio signal data which is sampled during a period between points of time t2 and t4 of FIG. 3 undergoes a signal processing operation carried out during a period between time points t4 and t6 according to a signal (g) shown in FIG. 3. The data is then recorded during a period between time points t6 and t7 according to a signal (h) of FIG. 3. More specifically, the data is recorded in the area CH2 of FIG. 2 while the head 3 is tracing the tape 1 from the point B to the point C of FIG. 1. Data which is sampled during another period between time points t4 and t7 is likewise recorded in the area CH2 by means of the head 4.
The signal or data which is thus recorded in the area CH2 is reproduced in the following manner: The data is read out from the tape 1 by means of the head 3 in accordance with the signal (h) of FIG. 3 during a period between points of time t6 and t7 (or between t1 and t2). The data thus read out is then subjected during a period between time points t7 and t8 (or t2 and t3) to a signal processing operation which is carried out according to a signal (i) shown in FIG. 3 in a manner reverse to the signal processing operation performed for recording. In other words, error correction, etc. are accomplished during this period. After completion of signal processing, a reproduced audio signal is produced according to a signal (j) shown in FIG. 3 during a period between points of time t8 and t9 (or t3 and t6). The reproducing operation with the head 4 is of course performed in exactly the same manner as the abovestated operation except that it is performed at a phase difference of 180 degrees. With the two heads used for reproduction in this manner, a reproduced audio signal is obtained in a continuous manner.
It goes without saying that, for each of other areas CH3 to CH6, the phase of the PG signal (a) is shifted to a degree of n.times.36.degree. as applicable and recording and reproducing operations are carried out in the same manner as described in the foregoing. These operations are independent of the travelling direction of the tape.
FIG. 4 shows a data matrix showing a format in which data is recorded in one track in each of the recording areas shown in FIG. 2. More specifically, this is an example of the data format including PCM audio data corresponding to the audio signal of two channels operating in a cycle of 1/60 sec. In the data matrix of FIG. 4, a column SYNC indicates a synchronizing data column; a column ADDRESS indicates an address data column; columns P and Q indicate error correcting redundant data columns respectively; a column CRCC indicates a known cyclic redundancy check code column; and columns D1 and D2 indicate data columns including audio signal information of the two channels respectively. Meanwhile, reference symbols b(0) to b(3x-1) denote lines of the data matrix respectively. Each of these lines forms a data block, in which data is recorded from the left-hand side to the right-hand side end of the line as viewed on the drawing one after another. For example, the data of the column ADDRESS in the line b(0) is recorded after the data of the column SYNC in the line b(0). Then, the data of the next column P in the same line b(0) is recorded after the data of the column ADDRESS and so on. After the data of the last column in the line b(l) is recorded the data of the column SYNC in the line b(l+1) is recorded. Data recording for one recording track comes to an end upon completion of recording the data of the last column in the last line b(3x-1).
Among the columns included in the group of columns D1, six data ID0 to ID5 on the lines b(0), b(1), b(x), b(x+1), b(2x) and b(2x+1) in the first column D1 are data carrying some additional information other than audio signal information. For example, the following additional information may be recorded in the positions of data ID0 to ID5: A mode information mark indicative of the travelling direction of the tape taken in recording or indicative of a track pitch which will be described later herein; a number assigned to an area to be used next time for recording; a length of time from the leader part of each program of the main information or from the end of the tape; and a program number or the like.
The apparatus of the kind mentioned in the foregoing is arranged to have two different recording/reproducing operation modes. One is a long play mode (hereinafter referred to as LP mode) in which the recording tracks are arranged to be formed at a narrower pitch than a standard track pitch for the purpose of performing recording and reproduction over a longer period of time than a standard operation. The other is a standard play mode (hereinafter referred to as SP mode) in which the recording tracks are formed at the standard track pitch for standard recording and reproduction. It is desirable to have some information on these modes recorded along with the audio data. In that instance, it is preferable to have two different recording and reproducing heads arranged, one for the SP mode and the other for the LP mode. Then, the data ID0 to ID5 of FIG. 4 may be used in recording mode information indicating the SP and LP modes.
In performing a recording operation with the tape recorder which is arranged as described above, the operator of the recorder selects (or designates) one of the areas in which recording is to be made. The additional information mentioned above then may be used for making this selection. In that instance, it is important for effective recording to first review before selecting a specific area all the information by reproducing the additional information about all the areas CH1 to CH6. For example, the travelling direction or speed of the tape is adjusted to a part already recorded or a part having a shorter length of time from the leader part among all the programs may be designated as an area to be used for recording. However, since there is no correlativity among the recording areas as mentioned in the foregoing, tracking control must be performed over all the areas one after another if all the additional information recorded along with the main information is to be reproduced. In that event, the recording operation not only requires an excessively long period of time but also necessitates an extremely complex logic arrangement for system control.
Further, it is impossible to quickly detect the additional information about all the areas for the whole length of the tape. It has been also impossible to look up desired additional information about all the areas, such as making a search for a part having a zero length of time from the leader part of a program.
In addition to these problems, there arises the following problem with regard to mode information on the SP and LP modes in cases where a part which has been recorded in the SP mode and another part having been recorded in the LP mode coexist in one and the same recording area: For recording by the so-called azimuth overlapped writing is reproduced using tracking control with tracking control pilot signals, the head must have the width thereof arranged to be wider than the track pitch. Let us assume that, during a reproducing operation on some area, the recording mode comes to change from the LP mode over to the SP mode and vice versa. In the event of the change to the SP mode while reproduction is being performed with the head for the LP mode, a record pattern formed in the SP mode is traced by the head for the LP mode. In this case, since the width of the LP mode head is generally arranged to be narrower than the pitch of tracks formed in the SP mode, the above-stated ID signal (or data) can be reproduced with a tracing action performed several times. Therefore, there arises no problem as it can be thus detected that the recording operation has been performed in the SP mode.
Whereas, in case that the record mode shifts to the LP mode during the process of reproduction in the SP mode, the record pattern formed in the LP mode comes to be traced by the head for the SP mode. Assuming that the travelling speed of the tape of the LP mode and that of the SP mode are in the ratio of 1:2 and that the head width of the SP mode head is 3/2 times as much as the pitch of the tracks formed in the SP mode, the head width of the SP mode head is three times as much as that of the LP mode head. Therefore, even in the case of azimuth recording, the head comes to produce reproduced signals simultaneously from two or more tracks. As a result, it becomes difficult to correctly reproduce the ID signals and to accurately detect that the information has been recorded in the LP mode.